Contact-less power transfer

Abstract

A system and method for transferring power does not require direct electrical conductive contacts. There is provided a primary unit having a power supply and a substantially laminar surface having at least one conductor that generates an electromagnetic field when a current flows therethrough and having an active area defined within a perimeter of the surface, the at least one conductor being arranged such that electromagnetic field lines generated by the at least one conductor are substantially parallel to the plane of the surface within the active area; and at least one secondary device including at least one conductor that may be wound about a core; wherein the active area has a perimeter large enough to surround the conductor or core of the at least one secondary device in any orientation thereof substantially parallel to the surface of the primary unit in the active area, such that when the at least one secondary device is placed on or in proximity to the active area in a predetermined orientation, the electromagnetic field induces a current in the at least one conductor of the at least one secondary device.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]The present application claims convention priority from UK patent applications numbers 0210886.8 filed on 13th May 2002, 0213024.3 filed on 7th Jun. 2002 and 0228425.5 filed on 6th Dec. 2002, all of which are incorporated herein by reference.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT[0002]Not applicableREFERENCE TO A “MICROFICHE APPENDIX”[0003]Not applicableBACKGROUND OF THE INVENTION[0004]1. Field of the Invention[0005]This invention relates to a new device and method for transferring power in a contact-less fashion.[0006]2. General Background of the Invention[0007]Many of today's portable devices incorporate “secondary” power cells which can be recharged, saving the user the cost and inconvenience of regularly having to purchase new cells. Example devices include cellular telephones, laptop computers, the Palm 500 series of Personal Digital Assistants, electric shavers and electric toothbrushes. In some of these dev...

AI Technical Summary

Benefits of technology

[0044]The at least one conductor in the primary unit may be a coil, for example in the form of a length of wire or a printed strip, or may be in the form of a conductive plate of appropriate configuration. A preferred material is copper, although other conductive materials may be used as appropriate. It is to be understood that the term “coil” is here intended to encompass any appropriate electrical conductor forming an electrical circuit through which current may flow and thus generate an electromagnetic field. In particular, the “coil” need not be wound about a core or former or the like, but may be a simple or complex loop or equivalent structure.

[0166]The problem with changing the operating frequency is that the secondary devices are typically configured to resonate at a predefined frequency. If the operating frequency changes, the secondary device would be detuned. To overcome this problem, we can change the capacitance instead of the operating frequency. The secondary devices can be designed such that each additional device placed in proximity to the primary unit will shift the inductance to a quantised level such that an appropriate capacitor can be switched in to make the circuit resonate at a predetermined frequency. Because of this shift in resonant frequency, the number of devices on the pad can be detected and the pad can also sense when something is brought near or taken away from the pad. If a magnetically permeable object other than a valid secondary device is placed in the vicinity of the pad, it is unlikely to shift the system to the predefined quantised level. In such circumstances, the system could automatically detune and reduce the current flowing into the coil.

Problems solved by technology

Many of today's portable devices incorporate “secondary” power cells which can be recharged, saving the user the cost and inconvenience of regularly having to purchase new cells.

There are a number of problems associated with conventional means of powering or charging these devices:Both the characteristics of the cells within each device and the means of connecting to them vary considerably from manufacturer to manufacturer, and from device to device.

If users are going away on travel, they will have to bring their collection of chargers if they expect to use their devices during this time.These adaptors and chargers often require users to plug a connector into the device or to place the device into a stand causing inconvenience.

If users fail to plug or place their device into a charger and it runs out of power, the device becomes useless and important data stored locally in the device might even be lost.In addition, most adaptors and chargers have to be plugged into mains sockets and hence if several are used together, they take up space in plug strips and create a messy and confusing tangle of wires.Besides the above problems with conventional methods of recharging devices, there are also practical problems associated with devices having an open electrical contact.

For example, devices cannot be used in wet environments due to the possibility of corroding or shorting out the contacts and also they cannot be used in flammable gaseous environments due to the possibility of creating electrical sparks.

However such chargers still suffer from all other problems as described above.

The adaptors are still only designed specifically for a certain make and model of device and are still only capable of charging one device at a time.

Whilst these universal chargers eliminate the need for having different chargers for different devices, they create even more inconvenience for the user in the sense that the battery packs first need to be removed, then the charger needs to be adjusted and the battery pack needs to be accurately positioned in or relative to the charger.

Although theoretically feasible, this method suffers from a number of drawbacks.

Firstly, the intensity of electromagnetic emissions is governed by regulatory limits.

This means that this method can only support power transfer at a low rate.

For example, data stored on credit cards maybe destroyed and objects made of metal will have induced therein eddy currents generating undesired heating effects.

Although this method provides a solution to the problems previously listed, it does so in a complicated and costly way.

The cost associated a multiple-coil system would severely limit the commercial applications of this concept.

Non-uniform field distribution is also a drawback.

None of the prior art solutions can satisfactorily address all of the problems that have been described.

Primary cells, or batteries of them, must be disposed of once used, which is expensive and environmentally unfriendly.

It is inconvenient for the user to have to either remove cells from the device for recharging, or to have to plug the device into an external power source for recharging in-situ.

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